The ink jet recording system is a recording system wherein ink droplets are discharged and jetted directly through very fine nozzles onto a recording member and allowed to adhere thereto to give letters and images. This system is widely used because of advantages not only in low noise and easy operation of a device used, but also in easy coloration and usability of paper as a recording member. As the ink used in an ink jet printer, a pigment-based ink is used in recent years in order to improve water resistance and light fastness.
However, the pigment is insoluble in a medium, and thus the pigment-based ink is easily agglomerated and often problematic in ink dispersion stability and jetting ability.
To improve the dispersion stability of pigment particles, Japanese Patent No. 2,512,861 and the equivalent thereto, U.S. Pat. No. 5,310,778, discloses techniques wherein a pigment and a water-soluble polymer are introduced into a roll mill and milled to give a dispersion of the pigment and water-soluble polymer dispersant prior to preparation of an ink liquid, Japanese Patent No. 2,919,045 and the equivalent thereto, U.S. Pat. No. 5,106,417, proposes a solid pigment preparation containing a carboxyl-containing polyacrylic resin, and JP-A 2002-20656 proposes use of a pigment milled in the presence of fine polymer particles dispersed in an aqueous medium.
JP-A 5-230390 and the equivalent thereto, U.S. Pat. No. 5,366,546, and WO-A 96/2302 and the equivalent thereto, U.S. Pat. No. 5,490,047, disclose a water-soluble polymer. JP-A 10-36732 discloses a dispersion in water of a pigment treated with rosin and microcapsulated.